Transcriptional regulation of gene expression in Tetrahymena thermophila.

The only well-characterized study of gene expression in Tetrahymena thermophila (1) demonstrates that the temperature dependent expression of the Ser H3 gene is regulated at the level of mRNA stability. A run-on transcription assay was developed to determine if regulation of RNA stability was a major mechanism regulating gene expression in Tetrahymena or if transcriptional regulation dominates. The relative transcriptional activities of 14 Tetrahymena genes were determined in different physiological/developmental states (growing, starved and conjugating) in which many of the genes showed striking differences in RNA abundance. In every case except Ser H3, changes in transcription accompanied changes in RNA abundance. Thus differential transcription, not differential RNA degradation, is the major mechanism regulating RNA abundance in Tetrahymena.